1. Field of the Invention
The present invention relates to a power line communication method for transmitting data signal with splitting of power transmission interval, particularly a power line communication method for transmitting power and data signals by splitting the entire interval for transmitting power and data signals into a power transmission interval and a data transmission interval.
2. Description of the Related Art
Power lines are equipments installed to supply power and their main objective is to supply power. Power line communication is carrying data signals on the voltage of power lines.
FIG. 1 is a waveform diagram illustrating the principle of power line communication of the related art.
As shown in FIG. 1, a power line communication carries data signals of low voltage having a frequency within several KHz˜several MHz on high AC voltage having a nominal frequency (60 Hz or 50 Hz for each country). Power line communication using an AC power line has several problems, such as attenuating data signals during transmitting the communication data signals through a transformer increasing or decreasing voltage in the AC power grid. It is one of the critical problems that errors occur in the communication data due to influence on the communication data from electrical noise signals generated from the load electric devices connected to the power lines.
Recently, power circuits that rapidly switch voltage ON and OFF have been widely used in electric products with development of power semiconductors; however, the electrical noise generated from switching the voltage influences the communication data at low voltage in the power line communication, which makes the problem worse.
Although power line communication using DC power lines is used when DC power grids are installed in predetermined sections, this communication also uses a method of carrying communication data signals at low voltage having a high frequency within several KHz˜several MHz on DC voltage, similar to the power line communication using AC power lines.
Although the DC power line communication does not attenuate the communication data signals through a transformer, as compared with when using the AC power lines, because it does not use a transformer, the electric noises generated from the load electric device connected to the DC power lines causes the same problems described above in the communication data signals, such that it has also a limit in use. The voltage magnitude of the electric noises influence the communication data signals at low voltage, such that the data signals are adjusted larger than the magnitude of the electric noises to reduce the influence due to the electric noises; however, it changes the amount of power to supply, such that this method is also necessarily limitative. Therefore, the power line communication of the related art has a problem in that data signals are influenced by the electric noises generated from the load electric devices and the transmitted data is lost, regardless of whether to use AC power lines or DC power lines.